Various abbreviations that appear in the specification and/or in the drawing figures are defined as follows:    ACK acknowledgment    BS base station    BWA broadband wireless access    CQI channel quality indicator    CQICH channel quality indicator channel    DL downlink (from BS to SS)    ID identification    IE information element    LA link adaptation    MAC medium access control (layer 2)    MAP media access protocol    NACK negative acknowledgment    OFDMA orthogonal frequency division multiple access    PHY physical (layer 1)    SS subscriber station (also referred to as a mobile station (MS))    UIUC uplink interval usage code    UL uplink (SS to BS)
The IEEE 802.16 working group has established a task group, 802.16m, to provide an advanced air interface which amends IEEE 802.16-2004, Air Interface for Fixed Broadband Wireless Access Systems, and also IEEE 802.16e, Air Interface for Fixed Broadband Wireless Access Systems, Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands and Corrigendum 1 (2005), in order to meet the requirements of next generation mobile networks. Reference may be had, for example, to IEEE 802.16 Broadband Wireless Access Working Group, IEEE 802.16m System Requirements, 2007-10-19.
The foregoing referenced IEEE 802.16 standards were designed to support fixed, nomadic and mobile clients in a BWA network. These standards provide different scheduling services to satisfy the demands for various multimedia services. Link adaptation is used to enhance spectrum efficiency. Since the LA is performed by the BS, for a DL transmission an UL fast-feedback channel is needed to transmit the CQI. The fast-feedback channel is a PHY channel that does not require MAC decoding. The goal is to provide a low latency CQI signaling technique.
A “semidynamic” technique to achieve a fast-feedback channel allocation has been adopted in current IEEE 802.16 systems. First, the BS sends an index to each SS (e.g., in a CQICH_Alloc_IE). If plural SSs have the same index they share the corresponding CQI channel. Then the BS dynamically allocates a fast-feedback region for every frame. Using the region information the SS can locate its own fast-feedback channel by using its own index. The index allocation may be considered as being semi-dynamic since related messages are designed to be transmitted only occasionally, while the fast-feedback region is allocated dynamically.
This type of semi-dynamic method is relatively simple to implement, and is a generally efficient way to allocate fast-feedback channels to SSs. However, it can be wasteful of the fast-feedback channels under certain conditions.
One condition of interest occurs when a particular SS stops using the fast-feedback channel. In the current method messages such as CQICH_alloc_IE are needed to adjust the index of other SSs accordingly to avoid generating gaps in the fast-feedback region (i.e., some feedback channels are not used). In some particular use cases, for example a Web browser that frequently starts or stops downlink transmission, such index allocations can be required frequently.
Another condition of interest concerns those SSs that may not require feedback at every frame. To accommodate this condition the CQICH control IE also assigns an interval number to SSs (e.g., 1, 2, 4, 8). However, this technique does not guarantee a full occupation of the fast-feedback region. For example, assume a case of five users with an interval of eight. In this case some feedback channels are not utilized, thereby wasting bandwidth.
In practice the semi-dynamic mechanism may at least partially address this second problem. For example, since the interval can only be 1, 2, 4, 8, the BS can ensure that the fast-feedback channel is not fully occupied. Then the dynamical fast-feedback region allocation can ensure that no channels are wasted.
However, when considering the first and second problems together this solution will result in large numbers of index adjust messages being sent, which in turn requires a large signaling overhead. For example, when a low index SS is present the BS needs to adjust a series of SSs indices.
To summarize, in IEEE 802.16e the SS is allocated a “CQICH channel allocation index” in the fast-feedback region for reporting CQI feedback, and a CQICH-Allocation IE is used for allocation and de-allocation of the fast-feedback channel. When the CQICH channel is once allocated it is fixed, and the SS reports periodic CQI feedback. No further signaling is transmitted. When the CQICH channel for a particular SS is allocated/de-allocated “holes” (unused UL bandwidth) can be created in the fast-feedback channel structure. If the presence of these holes is not addressed then resources are wasted. Alternatively, if some of the SS CQICH channels are reconfigured, then additional signaling overhead is required.
Selected portions of IEEE 802.16e, Air Interface for Fixed Broadband Wireless Access Systems, Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands and Corrigendum 1 (2005) that are of particular interest, and that are incorporated by reference herein, include pages 439-448 (including Sections 8.4.5.4.10, Fast-feedback channels, 8.4.5.4.10.1, Fast DL measurement feedback, 8.4.5.4.10.2, Fast MIMO feedback, 8.4.5.4.10.5, Enhanced Fast-feedback channels) and pages 468-471 (Section 8.4.5.4.12, CQICH Allocation IE Format).